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.TH TIMER_CREATE 3C "Oct 04, 2021"
.SH NAME
timer_create \- create a timer
.SH SYNOPSIS
.nf
#include <signal.h>
#include <time.h>

\fBint\fR \fBtimer_create\fR(\fBclockid_t\fR \fIclock_id\fR,
     \fBstruct sigevent *restrict\fR \fIevp\fR, \fBtimer_t *restrict\fR \fItimerid\fR);
.fi

.SH DESCRIPTION
The \fBtimer_create()\fR function creates a timer using the specified clock,
\fIclock_id\fR, as the timing base. The \fBtimer_create()\fR function returns,
in the location referenced by \fItimerid\fR, a timer \fBID\fR of type
\fBtimer_t\fR used to identify the timer in timer requests. This timer \fBID\fR
will be unique within the calling process until the timer is deleted. The
particular clock, \fIclock_id\fR, is defined in <\fBtime.h\fR>. The timer whose
\fBID\fR is returned will be in a disarmed state upon return from
\fBtimer_create()\fR, and can be started using \fBtimer_settime\fR(3C).
.LP
The \fIevp\fR argument, if non-null, points to a \fBsigevent\fR structure. This
structure, allocated by the application, defines the asynchronous notification
that will occur when the timer expires (see \fBsignal.h\fR(3HEAD) for event
notification details). If the \fIevp\fR argument is \fINULL\fR, the effect is
as if the \fIevp\fR argument pointed to a \fBsigevent\fR structure with the
\fBsigev_notify\fR member having the value \fBSIGEV_SIGNAL\fR, the
\fBsigev_signo\fR having the value \fBSIGALRM\fR, and the \fBsigev_value\fR
member having the value of the timer \fBID\fR.
.LP
The system defines a set of clocks that can be used as timing bases for
per-process timers. The following values for \fIclock_id\fR are supported:
.sp
.ne 2
.na
\fB\fBCLOCK_REALTIME\fR\fR
.ad
.RS 18n
wall clock
.RE

.sp
.ne 2
.na
\fB\fBCLOCK_HIGHRES\fR\fR
.ad
.RS 18n
non-adjustable, high-resolution clock
.RE

.sp
.LP
For timers created with a \fIclock_id\fR of \fBCLOCK_HIGHRES\fR, the system
will attempt to use an optimal hardware source. This may include, but is not
limited to, per-CPU timer sources.  The actual hardware source used is
transparent to the user and may change over the lifetime of the timer. For
example, if the caller that created the timer were to change its processor
binding or its processor set, the system may elect to drive the timer with a
hardware source  that better reflects the new binding. Timers based on a
\fIclock_id\fR of \fBCLOCK_HIGHRES\fR are ideally suited for interval timers
that have minimal jitter tolerance.
.LP
Timers are not inherited by a child process across a \fBfork\fR(2) and are
disarmed and deleted by a call to one of the \fBexec\fR functions (see
\fBexec\fR(2)).
.SH RETURN VALUES
Upon successful completion, \fBtimer_create()\fR returns \fB0\fR and updates
the location referenced by \fItimerid\fR to a \fBtimer_t\fR, which can be
passed to the per-process timer calls. If an error occurs, the function returns
\fB\(mi1\fR and sets \fBerrno\fR to indicate the error. The value of
\fItimerid\fR is undefined if an error occurs.
.SH ERRORS
The \fBtimer_create()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEAGAIN\fR\fR
.ad
.RS 10n
The system lacks sufficient signal queuing resources to honor the request, or
the calling process has already created all of the timers it is allowed by the
system.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The specified clock \fBID\fR, \fIclock_id\fR, is not defined.
.RE

.SH ATTRIBUTES
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
l | l
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
MT-Level	MT-Safe with exceptions
_
Standard	See \fBstandards\fR(7).
.TE

.SH SEE ALSO
.BR exec (2),
.BR fork (2),
.BR time (2),
.BR clock_settime (3C),
.BR signal (3C),
.BR timer_delete (3C),
.BR timer_settime (3C),
.BR signal.h (3HEAD),
.BR attributes (7),
.BR standards (7)
